In many database systems, data is stored and often updated at various points during the life of the data. This leads to a number of versions of a given set of data. Historically, a new or active version replaces a so-called previous version and it is not always possible to establish the content of the previous version once the new version has been stored. This is particularly the case in the travel environment, where customers purchase an airline ticket, for example and then wish to change the airline ticket at a later date.
It is well known that the tariff of an airline ticket will change between the date that the airline ticket becomes available and the date of travel. Accordingly, if the customer wishes to change the ticket at a certain point in time, the tariff may be different from the date on which the customer purchased the ticket. In this way the customer is either reimbursed at a level that is higher or lower than the purchase price but there is no guarantee that the customer is reimbursed at the level of the tariff on the date of purchase of the ticket.
US 2002/120648 (AT&T) discloses a method for accessing specific versions of documents and allowing the user to see the differences between the first and second version. An archive system makes copies of the different versions of the documents in order to keep them for any further requests from the user. The method also provides a system for comparing two different versions in order to point out the differences to the user. However, the only available version that is accessible to the user is the newest version; it is not possible to directly present the data content of a previous version to the user.